EP1050270A1 - Method and device for acquisition of electrocardiograms - Google Patents

Abstract

A first measuring loop (2,6) is applied to the heart of a patient (1) and a second measuring loop (4,6') is located nearby i the same disturbing electromagnetic field. Signals from the two loops (S1,S2) are combined in a summing or subtracting module (7) an the resulting signal (SR) is processed by a low pass filter (8), a frequency modulator (9) and an electro-optical convertor (10) before display (11)

Description

The present invention relates to the field of signal acquisition and processing physiological, in particular with a view to improving the ratio signal / noise, and relates to a method and a signal acquisition device electrocardiogram (ECG), substantially free of noise, especially noise from variations of the local magnetic field.

The acquisition of physiological signals poses often problems with faithful signal recovery, since generally weak and drowned in noise important.

The difficulty is further increased when the acquisition is carried out in an NMR environment and that the signal concerned is an electrocardiogram (ECG).

Now, the electrocardiogram is the signal physiological par excellence to monitor the state of a patient, but also as a signal of sequencing, in particular for an NMR imager, by example as a trigger signal of a acquisition sequence (better known as "triggering") and / or as a trigger signal an acquisition window (better known as designation "gating").

Indeed, this signal can be exploited from different ways, including visualization, shape analysis, counting or the like, with a view to determine morphological characteristics, frequency or whatever.

The EKG signal is a signal repetitive each sequence of which is made up of the juxtaposition of several waves (P, QRS, T, ST).

Signal denoising is of course important in terms of monitoring. Indeed, so that the doctor can follow the evolution of the patient, he must have clear access to the information and a noisy ECG does not appear to be of any utility.

Detecting peaks in the QRS complex is of paramount importance. On the one hand, for determine the heart rate but also for ability to synchronize the taking of images from an NMR imager on the ECG ("triggering" / "gating"). This synchronization cardiac makes it possible to excite each cut to a moment which is always the same in the cycle heart, and therefore to have an image of this cut which frees itself from the phenomena of movement.

Currently, this filtering phase of the EKG signal is usually performed by analog circuits or dedicated cards including characteristics are frozen and performance limited and fail to rid effectively the ECG signal from its artifacts and interference from electromagnetic interference prevailing in particular during NMR examinations.

These electromagnetic disturbances mostly come from peaks and changes premises of the main magnetic field Bo resulting from the action of the gradients implemented during NMR investigations. They introduce a signal of noise in the ECG signal measurement loop, of which the intensity can be equivalent to or even greater than that of the ECG signal.

Note that Bo is oriented along the axis longitudinal of the patient, in the case of an NMR device tunnel, and perpendicular to the coronal plane of the patient in the case of an NMR air gap device "open" type.

Considering that the orientation of the main field Bo corresponds to the Z axis of an orthogonal spatial coordinate system (X, Y, Z), the linear gradients in X, Y and Z can be defined as follows: grad.X = d Bz dx , grad.Y = d Bz dy and grad.Z = d Bz dz

To try to suppress this noise signal induced, several solutions have already been implemented artwork.

Thus, it was proposed to submit the ECG signal to a speed sensitive filter increase in signal voltage set to a value slightly higher than the maximum value typical of ECG dV / dt.

However, this process does not allow remove noise induced by sequences of applying and removing different gradients high frequency.

It was also proposed to derive the ECG signal taken from two secondary signals, delay one of these by a corresponding duration to a multiple of the ECG signal period and from extract the noise component, and then operate a subtraction between the non-delayed signal and the noise component of a previous period.

However, this process does not lead to a noticeable improvement in the ECG signal that if the induced noise, and therefore the conditions electromagnetic, are substantially identical on several periods of the ECG signal and if it is relatively regular. However, in practice, these cases do not are not common and this can result in noticeable distortion of the ECG signal.

The object of the present invention is in particular to overcome the aforementioned drawbacks.

To this end, it relates to a process acquisition of an electrocardiogram (ECG) of a patient in an electromagnetic environment disruptive, consisting in picking up on the patient a ECG signal with noise added to the region heart as a differential signal resulting from signals delivered by two electrodes forming part a first measurement loop, further comprising to be read simultaneously on the patient, in substantially identical disturbance conditions, a second measurement signal containing at least the noise, as a differential signal resulting from the signals delivered by two electrodes forming part of a second measurement loop separate from the first, then to add to or subtract from the first signal noisy ECG, in real time, said second signal measurement, depending on the polarity of the noise in this last with respect to noise in the ECG signal noisy and, finally, to treat, to convert, to transmit and / or display the resulting signal in real time, representative of the ECG and substantially devoid of noise.

• la figure 1 est une vue en perspective d'une tranche transversale d'un patient, à hauteur du coeur, illustrant l'implantation des électrodes selon une première variante de réalisation du procédé selon l'invention, en particulier par rapport au champ principal Bo dans un appareil RMN à tunnel ;
• la figure 2 est une vue schématique de dessus montrant la disposition des électrodes représentées à la figure 1 ;
• la figure 3 est une vue schématique de dessus illustrant une autre disposition des électrodes selon une deuxième variante de réalisation de l'invention ;
• la figure 4 est une vue schématique de dessus illustrant une autre disposition des électrodes selon une troisième variante de réalisation de l'invention ;
• la figure 5 est un schéma-bloc illustrant les différentes composantes d'un appareil d'acquisition de l'ECG selon un mode de réalisation particulier de l'invention ;
• les figures 6A et 6B sont des diagrammes temporels de signaux d'électrocardiogrammes recueillis durant l'application d'une séquence RMN, respectivement sans et avec mise en oeuvre du procédé selon l'invention, et,
• les figures 7A et 7B sont également des diagrammes temporels de signaux d'électrocardiogrammes recueillis avant et durant l'application d'une séquence RMN, respectivement sans et avec mise en oeuvre du procédé selon l'invention.

The invention will be better understood from the following description, which relates to preferred embodiments, given by way of nonlimiting examples, and explained with reference to the appended schematic drawings, in which:

• Figure 1 is a perspective view of a cross section of a patient, at heart height, illustrating the implantation of the electrodes according to a first embodiment of the method according to the invention, in particular with respect to the main field Bo in a tunnel NMR apparatus;
• Figure 2 is a schematic top view showing the arrangement of the electrodes shown in Figure 1;
• Figure 3 is a schematic top view illustrating another arrangement of the electrodes according to a second embodiment of the invention;
• Figure 4 is a schematic top view illustrating another arrangement of the electrodes according to a third embodiment of the invention;
• FIG. 5 is a block diagram illustrating the various components of an ECG acquisition apparatus according to a particular embodiment of the invention;
• FIGS. 6A and 6B are time diagrams of electrocardiogram signals collected during the application of an NMR sequence, respectively without and with implementation of the method according to the invention, and,
• FIGS. 7A and 7B are also time diagrams of electrocardiogram signals collected before and during the application of an NMR sequence, respectively without and with implementation of the method according to the invention.

So the process of acquiring the electrocardiogram (ECG) of a patient 1 located in a disruptive electromagnetic environment, consists first of all in recording said patient 1 a ECG signal plus noise S1 at the heart region as a differential signal resulting from the signals delivered by two electrodes 3, 3 'forming part of a first measurement loop 2.

According to the invention, said method consists, moreover, in simultaneously recording on the patient 1, in disturbed conditions substantially identical, a second measurement signal S2 containing at least noise, as a signal differential resulting from signals delivered by two electrodes 5, 5 'forming part of a second loop of measure 4 separate from the first 2, then add to or subtract from the first noisy ECG signal S1, in real time, said second measurement signal S2, in function of the noise polarity in the latter by relation to noise in the noisy ECG signal Si and, finally, to process, convert, transmit and / or display the SR Resulting Signal in real time, representative of the ECG and substantially devoid of noise.

To ensure presence in the signal resulting from at least one representative component of the ECG, it can be advantageously provided that the second measurement loop 4 is formed and arranged in such a way, that in case of acquisition by it a signal component representative of the ECG in more than or mixed with the noise signal, said signal component representative of the ECG present opposite polarity and / or amplitude less than that (s) of the signal component representative of the ECG collected by the first measurement loop 2.

Inspired in particular by the mode of creation and application of magnetic gradients during NMR experiments and the results of their actions cumulative in terms of creation and variation of intensities of local magnetic fields, the inventor been able to determine the measures to be taken to optimize the reduction of the signal component relative to noise induced by said gradients in the ECG signal resulting SR.

So, in the case of a patient 1 placed in a Nuclear Magnetic Resonance Imager or a analog NMR analyzer, dimensions apparent for magnetic flux, in a PP plane perpendicular to the direction of the main field Bo, first and second measurement loops 2 and 4 formed by the connecting wires 2 'and 4' of the electrodes 3, 3 'and 5.5' respectively and 2 ", 4" fabrics extending between the two electrodes 3, 3 '; 5.5 ' of the same measurement loop 2; 4 are determined for be similar, if not identical.

In this application context, the signal resulting SR can be advantageously used for monitoring by patient monitoring and for triggering of IRMN ("triggering" and / or "gating").

As appears from a comparison between Figures 1 and 2 of the accompanying drawings, on the one hand, and the Figures 3 and 4, on the other hand, the two loops of measures 2 and 4 may, depending on the applications and the constitution of the sensor means used, or be physically separate and independent, either have a common electrode 3 ', 5'.

According to a first embodiment of the invention, the first and second loops of measures 2 and 4 are arranged substantially symmetrically to the patient's midplane PM 1 perpendicular to the PC coronal plane of the latter, the electrodes 3, 3 '; 5, 5 'of the two measurement loops 2 and 4 being preferably but not necessarily arranged in alignment and presenting a similar spacing between the electrodes of each pair 3 and 3 '; 5 and 5 '(see Figures 1 to 3 and 5 of attached drawings).

Indeed, the inventor was able to observe that the noise signals detected by measurement loops 2 and 4 configured and arranged as described above were substantially identical under the common NMR experiments using gradients magnetic field.

According to a second embodiment of the invention shown in Figure 4, the three electrodes 3, 3 '; 5, 5 'forming the two loops of measures 2 and 4 are arranged in a configuration triangular at the level of the cardiac region of such so that the second measurement loop 4 detects a signal component representative of the ECG of opposite polarity and amplitude substantially equal to that of the signal component representative of the ECG recorded by the first measurement loop 2.

Finally, with a view to its exploitation in time real, especially in the context of monitoring the condition of a patient undergoing NMR examination, the signal SR resulting from the addition or subtraction of differential signals S1 and S2 delivered by the two measurement loops 2 and 4 can be processed by a filter low pass 8, then used for modulation in frequency of a carrier and finally transmitted to a apparatus 11 provided with means for displaying the ECG signal SR filtered, if necessary after conversion to signal optical.

The ECG signal can be expected to be possibly subject to digital filtering by a infinite impulse response filter of the type elliptical or called Cauer's, for example from the fourth order.

The present invention also relates to a sensor device for real-time acquisition of the ECG signal of a patient 1, in particular subject to an NMR examination, which can be linked to a device display 11 and in particular allowing the setting work of the method as described above.

This system mainly consists of, on the one hand, by two modules 6, 6 'of sampling physiological signals S1 and S2 provided by two separate measurement loops 2 and 4 each comprising a pair of electrodes 3, 3 '; 5, 5 'placed on the patient 1, at least one of the two signals physiological S1, S2 including a component of signal representative of the ECG, on the other hand, by a module 7 summing or differentiating signals S1 and S2 delivered by the two sampling modules 6, 6 ' and, finally, by processing modules 8, 9, 10, including filtering and conversion of the SR signal provided by said module 7 summing or differentiating.

The sampling modules 6, 6 'consist advantageously, each one, in an amplifier instrumentation differential whose inputs are connected to the respective electrodes.

The processing modules 8, 9, 10 can for example consist respectively of a filter low pass 8, in a frequency modulation unit 9 and into an electro-optical conversion module 10 connected to an optical fiber whose other end is connected to an 11 'opto-electronic conversion module connected or forming part of the apparatus 11 provided with the means ECG signal display.

Advantageously, all of the modules 6, 6 ', 7, 8, 9, 10 are grouped in an armored box 12 forming a Faraday cage, which is connected to the electrodes 3, 3 '; 5, 5 'by connecting wires resistive flexible 2 ", 4" and which is not in contact directly with the skin of patient 1, the two modules of sample 6, 6 'which may optionally include a common electrode 3 ', 5'.

In addition, the various elements and parts forming the device according to the invention could be essentially made from materials non-magnetic, making its use perfectly compatible with a sensitive magnetic environment and disruptive.

The device for implementing the acquisition process described above may in particular consist of a sensor device of the type described in French Patent No. 2,704,131 or in the patent French No. 2,729,071.

The advantages provided by the invention, in term for improving the quality of the ECG signal final, appear very clearly to the study of Figures 6A, 6B, 7A and 7B of the accompanying drawings.

FIGS. 6A and 6B, on the one hand, and 7A and 7B, on the other hand, represent signals electrocardiograms collected from the same patient and under the same conditions of positioning of electrodes and electromagnetic environment.

So these signals were collected with a placement of the electrodes approximately 22 cm in front of the magnetic center, which constitutes positioning most unfavorable (disturbances due to switching of the gradients being maximum), and with magnitude gradients 16 mT / m.

The signals of Figures 6A and 6B have been collected during the application of an NMR sequence of the type known as "Fast Spin Echo", whereas the signals of FIGS. 7A and 7B have been collected before and during the application of a sequence NMR of the type known as "Echo of Gradient "with flow compensation.

Improving signal quality resulting from the application of the method according to the invention clearly appears by comparing, on the one hand, the figure 6A with FIG. 6B and, on the other hand, FIG. 7A with Figure 7B.

The invention remains valid even if the electrode arrangement changes.

Of course, the invention is not limited to the embodiments described and shown in attached drawings. Modifications are still possible, especially from the point of view of the constitution of the various elements or by substitution of technical equivalents, without going beyond the protection of the invention.

Claims (12)

Electrocardiogram acquisition process (ECG) of a patient located in a disruptive electromagnetic environment, consisting of reading an ECG signal on the patient added noise to the heart region in as a differential signal resulting from the signals delivered by two electrodes forming part of a first measurement loop, characterized in that it consists, moreover, in simultaneously recording on the patient (1), in disturbed conditions substantially identical, a second measurement signal (S2) containing at least noise, as a signal differential resulting from signals delivered by two electrodes (5, 5 ') forming part of a second loop measurement (4) separate from the first (2), then add to or subtract from the first ECG signal noisy (S1), in real time, said second signal measurement (S2), as a function of the polarity of the noise in the latter with respect to the noise in the ECG signal noise (S1) and, finally, to treat, convert, transmit and / or display the signal in real time resulting (SR), representative of the ECG and significantly devoid of noise. Acquisition process according to claim 1, characterized in that the second measuring loop (4) is made up and arranged with in such a way that if it acquires a signal component representative of the ECG in addition to the or mixed with the noise signal, said component of signal representative of the ECG has a polarity opposite and / or an amplitude lower than that (s) of the signal component representative of the collected ECG by the first measurement loop (2). Acquisition method according to one any of claims 1 and 2, characterized in that in the case of a patient (1) located in an Imager Nuclear Magnetic Resonance or device analog NMR analysis, the apparent dimensions for the magnetic flux, in a plane (PP) perpendicular to the direction of the main field (Bo), the first and second measurement loops (2 and 4) formed by the wires of connection (2 'and 4') of the respective electrodes (3, 3 ' and 5, 5 ') and the tissues (2 ", 4") extending between the two electrodes (3, 3 '; 5, 5') of the same loop measure (2; 4) are similar, even identical. Acquisition method according to one any one of claims 1 to 3, characterized in that that the first and second measurement loops (2 and 4) have a common electrode (3 ', 5'). Acquisition method according to one any of claims 1 to 4, characterized in that the first and second measurement loops (2 and 4) passing through the electrodes are arranged substantially symmetrically with respect to the median plane (PM) of the patient (1) perpendicular to the coronal plane (PC) of this latest. Acquisition process according to claim 5, characterized in that the electrodes (3, 3 '; 5 5') separate or with a common electrode two measuring loops (2 and 4) are arranged aligned way. Acquisition method according to one any of claims 1 to 4, characterized in that the three electrodes (3, 3 '; 5, 5') forming the two measuring loops (2 and 4) are arranged in a triangular configuration at regional level cardiac so that the second loop of measure (4) reads a signal component representative of the ECG of opposite polarity and amplitude substantially equal to that of the component signal representative of the ECG recorded by the first measurement loop (2). Acquisition method according to one any one of claims 1 to 7, characterized in that that the signal (SR) resulting from the addition or subtraction of differential signals (S1 and S2) delivered by the two measurement loops (2 and 4) is processed by a low-pass filter (8), then used to the frequency modulation of a carrier and, finally, transmitted to an apparatus (11) provided with means display of filtered ECG (SR) signal, if applicable after conversion to optical signal. Sensor device for acquisition in real-time signal from a patient's ECG, especially subjected to an NMR examination, which can be linked to a display device and allowing in particular the setting work of the process according to any one of claims 1 to 8, characterized in that it is mainly consisting, on the one hand, of two modules (6, 6 ') for sampling physiological signals (S1 and S2) supplied by two separate measurement loops (2 and 4) each comprising a pair of electrodes (3, 3 '; 5, 5 ') placed on the patient (1), at least one of two physiological signals (S1, S2) comprising a signal component representative of ECG, other part, by a summing or differentiating module (7) signals (S1 and S2) delivered by the two modules sampling (6, 6 ') and, finally, by modules (8, 9, 10) processing, including filtering and conversion of the signal (SR) supplied by said module (7) summator or differentiator. Device according to claim 9, characterized in that all the modules (6, 6 ', 7, 8, 9, 10) are grouped in an armored box (12) forming Faraday cage, which is connected to the electrodes (3, 3 '; 5, 5 ') by flexible resistive connecting wires (2 ", 4 ") and which is not in direct contact with the skin of the patient (1). Device according to any one of claims 9 and 10, characterized in that both sampling modules (6, 6 ') have an electrode common (3 ', 5'). Device according to any one of claims 9 to 11, characterized in that the different elements and parts forming said device are essentially made from materials non-magnetic, making its use perfectly compatible with a sensitive magnetic environment and disruptive.

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